1. Field of the Invention
This invention relates to a method of producing L-serine, and more specifically, to a method of producing L-serine from glycine and formaldehyde under the existence of a microorganism having the ability of producing serine hydroxymethyltransferase.
2. Description of the Background Art
L-serine is important as an amino acid as well as drugs, cosmetics, feed additives and intermediate for drugs.
Serine hydroxymethyltransferase (E.C.2.1.2.1.) also called as either serine transhydroxymethylase or serine aldolase, widely exists in mammals, birds, higher plants, microorganisms and so forth. It is already known to catalize the reaction of synthesizing a .beta.-hydroxyamino acid from glycine and an aldehyde carried out using pyridoxal phosphate as a coenzyme. (for example, Advances in Enzymology 53, 83-112 (1982)).
Conventionally, as a method of producing L-serine by an enzymatic method utilizing the serine hydroxymethyltransferase of a microorganism, a method of producing L-serine from either glycine alone or the combination of glycine and a minute amount of formaldehyde by using a microorganism belonging to the Proteus (Patent Publication No. 58-2677 (1983)), the Sarcina, the Flavobacterium, the Pseudomonas or the Microbacterium (Patent Laid-open No. 53-81691 (1978)) genus has been known. Every microorganism utilized in such a method has a strong activity of producing L-serine from glycine itself. Even when formaldehyde is added to prepare reaction solution, the molar ratio of L-serine produced to formaldehyde added in the reaction is only around 10 to 1. This is understood to indicate that not only serine hydroxymethyltransferase but also an enzyme catalyzing the reaction of cleaving glycine intensely participates in the reaction resulting in an extremely low yield of L-serine relative to glycine of 10% mole/mole or less. Here, since the accumulated concentration of L-serine is around 5 g/l at the most, it is hard to say that this method is a practical one.